KR20130020913A - Method and apparatus for homogenising and stabilising an iron-bearing residue - Google Patents

Abstract

A method and apparatus are disclosed for converting iron-containing residues produced in a wet smelting process and containing small amounts of soluble heavy metals into stable forms using neutralizing agents. The residue is washed, the washed residue is fed onto at least one stabilization or homogenization reactor, in which a neutralizing agent is also introduced, and the homogeneous mixing of the residue and the neutralizing agent is carried out using a spiral mixer (8). Wherein the ratio of the diameter of the mixer to the diameter of the reactor is 0.75 to 0.99.

Description

METHOD AND APPARATUS FOR HOMOGENISING AND STABILISING AN IRON-BEARING RESIDUE

The present invention relates to a method and apparatus for converting iron-containing residues comprising small amounts of soluble heavy metals produced in a wet smelting process into stable forms using neutralizing agents. The residue is elutriated, and this washed residue is fed into at least one stabilization and homogenization reactor, into which also a neutralizer is added. Homogeneous mixing of the residue and the neutralizing agent is done using a helix mixer, where the diameter of the mixer relative to the diameter of the reactor is 0.75 to 0.99.

Solid wastes produced in wet smelting processes, such as various kinds of iron precipitates and leach residues, generally contain small amounts of soluble heavy metals such as zinc, cadmium, cobalt, nickel, arsenic and antimony. This kind of residue requires pretreatment, in which the residue is stabilized before it is buried in landfills so that heavy metals do not dissolve from the waste. Known pretreatment methods carried out alone or in combination are, for example, waste washing, neutralization and precipitation of metals as hydroxides, precipitation of metals as sulfides, isolation of waste treatment plants from groundwater and, for example, cement, phosphate Or binding soluble compounds with lime.

Sulfide precipitation is one effective method for binding heavy metals, but the additional costs incurred by this method as well as the large amounts of water that migrate to landfills can be considered a weakness. Due to the large amount of water involved, the landfill must have a multi-layered wall and intake system to prevent landfill water from penetrating into the groundwater.

The zinc production process is a typical process in which iron-containing waste is produced. The production process derived from the zinc sulfide concentrate according to one production method comprises roasting of the concentrate, calcination, ie leaching of the obtained zinc oxide, in which zinc oxide is sulfuric acid Leaching using a solution containing to form zinc sulfate in the so-called neutral leaching. Zinc sulfate solution is generally added to the electrolytic recovery via solution purification. The insoluble residue of neutral leaching consists of zinc ferrite and sulfur formed in roasting, which residue is treated in a strong acid leaching step to leach the ferrite, which results in the recovery of zinc bound to the ferrite. Iron is precipitated as jarosite, goethite or hematite, usually as jarosite. This residue is often floated to separate sulfur from iron deposits. Zinc sulfide concentrates can also be introduced, for example, into a strong acid leaching step without roasting, or the leaching of the whole concentrate can be carried out without roasting, and the resulting waste residues comprise both iron and sulfur of the concentrate.

Disposal of iron residues produced in the zinc concentrate and other equivalent metal leaching processes should be done so that the final residue or reject is as low as possible so that any residue that may remain in the iron residues Small amounts of heavy metal residues do not cause problems. Hematite is extremely poorly soluble but its production generally requires autoclave conditions, which increases the cost of the process.

Conventionally, for example, CA 1079496 and Part VII of the literature published by Ek, C. at the International Symposium on the Control of Iron in Wet Refining held October 19-22, 1986 in Toronto, 719-729. Attempts have been made to solve the problem of the storage of iron residues as presented in "Jarosite Treatment and Disposal by the Jarochaux Process" of Cotton. According to this method, iron residues, which may be jarosite or other possible iron compounds, are mixed with calcium compounds. This calcium compound may be quicklime, hydrated lime or lime oil, for example. As a result of the physicochemical reaction, spherical lumps having a diameter of 1 to 20 cm are formed. Sulfates in the iron residue react with calcium to form gypsum, which in turn forms a skeleton in the jarosite ingot and a shell around the ingot. The method consists of the following steps: The first step is a filtration step, followed by a washing step to a solids content of about 50 g / l, after this concentration and backflow of the concentrator (about 200 g / l solids) Content), then the air drying step of the residue on the filter, and the water content after the air drying step is about 35%. The residue from the filter is fed to the screw mixer by a belt conveyor, and finely divided lime is also fed into the screw mixer. If the iron residue is mainly jarosite, the amount of lime (CaO) to be added is 6-16% of the amount of dry solids of the waste residue. If this waste residue is a getite, the amount of lime required is less. According to an embodiment of this patent publication, the mixing reactor for residue and lime is a washing machine shape and is equipped with two blade mixers which rotate in opposite directions.

According to the method described in IT 1290886, wastes comprising heavy metals are stabilized by adding calcium hydroxide, orthophosphoric acid or salts thereof in the waste as an aqueous solution and, if necessary, by adding water to obtain a paste of uniform consistency. The drawback of this method is that the waste must be dried before it is landfilled.

Lime neutralization is suitable for almost all types of waste and even old landfills can be treated by the addition of lime. However, this method has the disadvantage that the waste produced does not have a uniform quality. As a result of non-uniform neutralization, some of the material remains unneutralized, and in some of the material the pH rises too high, causing decomposition of jarosite.

Another method aimed at the disposal of iron residues, in particular jarosite, is the Jarofix process, which is described, for example, in Seyer, S. et al. Disposal measures "(JOM, Dec. 2001, p. 32-35). The initial part of the process is similar to that of the jaroshow process described above, i.e., the jarosite residue is washed and concentrated, and lime is mixed into the residue, but afterwards the cement is used to bind the residue. Is added to. Cement allows long-term physical and chemical stabilization of iron residues. Of course, the use of cement as a binder stabilizes the jarosite well, but this also incurs additional costs for the process.

FI 84787 discloses a mixing reactor and a mixer located in the mixing reactor, the apparatus aiming to mix two liquids with each other or to mix liquids and solids, and at the same time to separate other liquids or solids from the liquids. . The apparatus consists of a reactor consisting of three parts of a cylindrical upper part, a conical part below it, and a lowermost tubular collecting part. Baffles are located on the edge of this reactor. The mixer consists of two tubular coils surrounding the shaft and a protective cone which is fixed within the bottom of the mixer, the protective cone aiming to prevent flow from entering the reaction zone and aspiration of the droplets upwards. It is done. The diameter of the mixer is 0.5 to 0.75 times the diameter of the reactor, which means that the zone in which it is actually stirred is only half of the volume of the reactor. This mixer also extends into the cone of the reactor, and correspondingly the distance from the mixer shaft of the tubular coil is reduced so that the ratio of the diameter of the mixer to the diameter of the reactor is maintained at the above mentioned level. The reactor and mixer are aimed at mixing two liquids or mixing liquids and solids, and the description of this plant reveals that the solids content of any slurry that can be produced is not very high. Mixing in the lower part of the mixer is weaker, so the phases separate after the reaction that occurs during mixing. At the bottom of the reactor, the goal is to prevent solids from moving to the top of the reactor.

It is an object of the present invention provided herein to eliminate the drawbacks of the process described above, and to form a uniform quality reject paste with a very high solids content that is easy to collect from iron residues using neutralizing agents. To disclose a method and apparatus. If no harmful compound is present in the reject, this waste can be used, for example, as a soil enhancer. After treatment, the homogeneous reject paste is transported directly to the storage site where the waste paste solidifies into a mass of solids where no separation of the solution from the mass to the storage site occurs. According to this method, a further benefit of the stabilized material is that the contact area between rainwater and this stabilized reject paste is considerably smaller than for pulverized or finely divided waste.

The present invention relates to a process for converting iron-containing residues produced in a wet smelting process and containing small amounts of soluble heavy metals into a stable form using neutralizing agents, the residues being primarily washed. The residue washed is fed into at least one stabilization or homogenization reactor, a neutralizing agent is also introduced into the stabilization or homogenization reactor, and homogeneous mixing of the cavity with the residue is carried out using a spiral mixer, The ratio of the diameter of the mixer to the diameter of the reactor is 0.75 to 0.99.

According to one embodiment of the invention, said neutralizing agent is supplied in said stabilizing reactor in powder form.

According to another embodiment of the invention, the neutralizing agent is fed into the stabilization reactor in the form of a slurry.

In the process according to the invention, the neutralizing agent is typically a calcium and / or magnesium compound.

The present invention also relates to an apparatus for converting iron-containing residues produced in a wet smelting process and containing small amounts of soluble heavy metals into a stable form using neutralizing agents, which residues are first washed in a washing reactor. The residue that has been cleaned is introduced into at least one stabilization or homogenization reactor, the upper part of the homogenization reactor is cylindrical, the lower part is shaped like a cone narrowing downwards, and the residue and neutralizing agent are in the upper part of the reactor. Supplied, homogenized paste is removed from the bottom of the reactor; The reactor has a mixer, the mixer comprising at least two spiral bars surrounding the shaft and supported on the shaft using support arms, the spiral bars being located symmetrically with each other and the stabilizing or homogenizing reactor The ratio of the diameter of the mixer to the diameter of is 0.75 ~ 0.99.

According to one embodiment of the invention, the mixer consists of two parts, the upper mixer part being equal to the stabilizing or homogenizing, wherein the distance of the spiral bar of the mixer from the shaft is equal throughout the height of the mixer part. The lower mixer portion, which is installed in the cylindrical portion of the reactor and whose distance of the spiral bar of the mixer from the shaft becomes smaller conically toward the bottom of the mixer, is in the portion of the reactor that is shaped like a conical narrowing downward. Is located.

According to one embodiment of the invention, the number of said support arms for supporting said spiral bars at different heights is 4-8. The support arms in the mixer are typically at an angle of 0 to 65 ° with respect to the horizontal, depending on the position of the support arm in the mixer or mixer portion.

When the mixer according to the invention consists of two parts, the spiral bars of the upper and lower mixer parts are preferably offset relative to one another.

The spiral bar of the device according to the invention encloses the shaft 0.5 to 2 times, and the angle of the pitch of the spiral bar is 15 to 45 °, preferably 25 to 35 ° with respect to the horizontal.

According to one embodiment of the invention, the ratio of the diameter of the mixer to the diameter of the stabilization reactor is between 0.85 and 0.95.

According to one configuration of the apparatus according to the invention, the guide plates directed inclined inwardly from the edge of the reactor are installed in the upper part of the neutralization reactor to guide slurry flow, and 3 to 8% of the diameter of the reactor. Extend inward by a distance of.

1 shows a flow chart of a process,
2 is a longitudinal sectional view of the stirred reactor and mixer according to the present invention.

The present invention relates to a method and apparatus for neutralizing and stabilizing waste residues comprising iron and small amounts of heavy metals. According to the present invention, the waste residue is stabilized with a homogeneous reject paste so that the entire mass formed is of uniform size and stabilized by a method other than just forming a shell and skeleton of lime. Occurs. This waste residue may comprise, in addition to jarosite type iron residues, for example, sulfur containing residues produced in the direct leaching of zinc. In addition to jarosite, iron residues may also consist of other iron compounds such as getite or hydroxides. Iron-containing waste residues may be derived from processes other than the zinc production process, although it has been found that the zinc production process is particularly suitable for this iron-containing waste residue. Since this reject paste contains no harmful compounds at all, it can be used, for example, as a soil enhancer.

As used herein, the terms neutralization reactor and stabilization reactor mean the same reactor, and likewise the neutralizer and stabilizer mean the same material.

A simple process diagram of the method is shown in FIG. In the first step of the process, the filter cake of the waste residue 1 is washed in the washing reactor 2 to become a homogeneous slurry. Depending on the moisture content of the residue, the washing can be carried out in the water contained in the residue to be filtered or by supplying additional water. The washed residue is fed into a stabilization or homogenization reactor 3, for example using a hose pump, where neutralization is carried out using a suitable neutralizing agent or stabilizer 4, such as a suitable calcium and / or magnesium compound. All. Stabilizers are determined by the composition of the waste to be treated. Stabilizers can be supplied in a dry state or as an aqueous slurry, preferably supplied inside the slurry. In addition to the drying stabilizer, water may also be supplied into the reactor as needed. One or several stabilization reactors may be provided. The stabilized homogeneous reject paste 6 is removed from the bottom of the reactor, for example using a hose pump.

In the first step of the process according to the invention, the residue exiting the filter is washed in the washing reactor 2 to become a homogeneous slurry. At this stage no stabilizer is added. In this way, it can be ensured that the waste to be stabilized is always of uniform quality before contact with the stabilizer. For this reason, the reaction between waste and stabilizer in a stabilization reactor can occur in a controlled manner. The method according to the invention makes it possible to eliminate the drawbacks in the above-described method, such as the pH change caused by non-uniform neutralization. Too high a pH value can lead to degradation of the material to be stabilized, for example jarrosite.

A homogeneous reject paste can be obtained by a controlled stabilization reaction, which can be transported directly to landfill, where the reject paste has no separation of solution from the mass at the waste disposal plant. Solidifies into a mass of solids. In the method described above, incompletely controlled reactions lead to the production of non-uniform ingots which may have diameters on the order of 20 cm and on the other hand finely divided ground material. According to this method, a further advantage of stabilized homogeneous materials is that the contact area between rainwater and stabilized waste is considerably smaller than that of crushed or finely divided waste.

As shown in more detail in FIG. 2, it is preferable that the upper part 5 of the stabilization reactor 3 consists of a vertical cylindrical part, and the lower part 6 consists of a conical part narrowing downward. It is preferable that the angle of a cone is 45-75. The slurry to be neutralized is supplied in the upper part of the reactor, in which it is advantageous for the guide plates 7 to be installed to guide the fluid towards the center. These plates extend inwardly from the edge of the reactor by a distance of about 3-8% of the diameter of the reactor. The neutralized and stabilized reject paste is removed from the bottom of the conical bottom by gravity or by force. This neutralization reactor is provided with a mixer 8, which is two parts consisting of an upper mixing section 9 and a lower mixing section 10 in the embodiment shown in FIG. 2. Both parts of the mixer are attached to the same vertical shaft 11. According to a second embodiment, the mixer parts are integral.

The (both) portions of the mixer consist of at least two spiral bars 12, 13 which surround the shaft and are supported on the shaft. These spiral bars are installed symmetrically with each other so that the distance from the shaft is the same when viewed from the same height. The angle of the pitch of the spiral bars is 15 to 45 degrees, preferably 25 to 35 degrees with respect to the horizontal. The helical bar is supported on the shaft 11 by support arms 14, which are located at two to six different heights within each mixer part, depending on the height of the mixer part. In particular, the number of support arms in the upper part is about 3-6. If the mixer is one part, the support arms are located at four to eight different heights. In each mixer portion, the support arms are at an angle of 0 to 65 ° with respect to the horizontal, depending on the position of the support arms in the mixer. The support arms act not only as support elements for the spiral bars, but also as mixing elements in the central part of the reactor, which support arms facilitate the realization of homogeneous mixing.

The distance of the spiral bar from the shaft in the upper mixer portion is the same throughout the mixer portion, while the distance of the spiral bar from the shaft in the lower mixer portion decreases conically toward the lower portion of the mixer. The mixer 8 is installed in the reactor 3 such that the lower conical mixer portion 10 is located in the cone 6 of the reactor. If the mixer is integral, the spiral bar is continuous from bottom to top. If the mixer consists of two mixer parts, the spiral bar in the lower mixer part is preferably offset with respect to the spiral bar of the upper mixer part. The ratio of the diameter of the mixer or mixer parts to the diameter of the reactor is about 0.75 to 0.99, preferably 0.85 to 0.95 so that the entirety of the material in the reactor is uniformly mixed.

Since the mixed materials are paste-like, or the neutralizing agent is a pulverized solid, and the product to be produced is paste-like, no baffle or protective cone is provided in the stabilization reactor. Depending on the height of the reactor, the spiral bar surrounds the shaft 0.5 to 2 times. The mixer is preferably coated with some suitable non-viscous material such as Teflon.

As a result of the tests conducted, a mixer consisting of a spiral bar and its supporting arms results in a very homogeneous mass of the neutralizing agent to be mixed with the iron residue to be treated, in which the individual particles of iron residue and neutralizing agent are distinguished. It turns out that it can't be. Likewise, the waste residues formed are very stable, so that the amount of heavy metals dissolved in these waste residues is less than the value of the established guidelines.

Example

Example 1

The filter cake of the waste residue comprising jarosite and elemental sulfur was rinsed in the washing reactor to become a homogeneous slurry. The moisture content of the waste residue was 39%. This slurry was pumped at 120 L / h from the scrubbing reactor to the stabilization reactor, and 29 kg / h of calcium hydroxide was fed into the stabilization reactor. 8 L / h of water was fed into the stabilization reactor during the supply of calcium hydroxide. The effective volume of the stabilization reactor was 30 dm ³ . Stabilization was performed at room temperature. This continuous experiment lasted for 5 hours. During the experiment, 200 L of stabilized waste formed was collected in the vessel. Samples were collected from the stabilized waste during the experiment. This stabilized material was poured onto a flat base where the behavior of the material was examined. This material was left overnight to solidify. This material solidified and no water was discharged from it. The individual particles of iron residue and neutralizer in the divided and solidified pieces were indistinguishable. Solubility tests in accordance with EU standard EN-12457-3 were carried out on the solidified and stabilized reject paste. Experimental results were below the hazardous waste limits set by the EU Directive.

Example 2

In this embodiment, one of the above experimental configurations was repeated, the other being that the stabilization reactor according to the invention was replaced with a skew mixer. As a result, a lumpy, heterogeneous waste was obtained, and unreacted lime could be detected clearly.

Claims (13)

A process for converting iron-containing residues produced in a wet smelting process and containing a small amount of soluble heavy metals into a stable form using a neutralizing agent, wherein the residues are first elutriated (2) and the residues cleaned Water is fed into at least one stabilization or homogenization reactor 3, also into the stabilization or homogenization reactor 3, a neutralizer 4 is introduced, and the homogeneous mixing of the residue and the neutralizer is carried out in a spiral mixer ( 8), wherein the ratio of the diameter of the mixer 8 to the diameter of the reactor 3 is 0.75 to 0.99, for converting the iron-containing residue into a stable form using a neutralizing agent. Way. The method of claim 1,
Wherein said neutralizing agent is fed into said stabilization or homogenization reactor in powder form, wherein said iron-containing residue is converted into a stable form using neutralizing agents. The method of claim 1,
Wherein said neutralizing agent is fed into said stabilization or homogenization reactor in the form of a slurry. The method of claim 1,
Wherein said neutralizing agent is a calcium and / or magnesium compound, wherein said iron-containing residue is converted into a stable form using said neutralizing agent. An apparatus for converting iron-containing residues produced in a wet smelting process and containing a small amount of soluble heavy metals into a stable form using a neutralizing agent, wherein the residues are first washed in the washing reactor (2) and washed. The residue is introduced into at least one stabilization or homogenization reactor 3, the upper part 5 of the stabilization or homogenization reactor is cylindrical, and the lower part 6 is conical shaped like a narrowing downward, and the residual Water and neutralizing agent are supplied in the upper part of the reactor, and the homogenized paste is removed from the lower part of the reactor; The reactor has a mixer 8, which combines at least two helical bars 12, 13 which surround the shaft and are supported on the shaft 11 with support arms 14. Wherein the spiral bars are positioned symmetrically to each other and the ratio of the diameter of the mixer to the diameter of the stabilization or homogenization reactor is 0.75 to 0.99, in a stable form using a neutralizing agent. Device for switching. The method of claim 5, wherein
The mixer 8 consists of two parts 9, 10, the distance of the spiral bars 12, 13 of the mixer 8 from the shaft 11 over the entire height of the mixer part. The same upper mixer part 9 is installed in the cylindrical part 5 of the stabilization or homogenization reactor, with the distance of the helical bars 12, 13 of the mixer 8 from the shaft towards the bottom of the mixer. A lower mixer portion (10) that becomes smaller conical is located in the portion of the reactor that is shaped like a conical narrowing downwardly, wherein the iron-containing residue is converted into a stable form using a neutralizing agent. The method according to claim 5 or 6,
Apparatus for converting iron-containing residues into a stable form using neutralizing agents, characterized in that the number of said support arms (14) supporting said spiral bars (12, 13) at different heights is four to eight. The method according to claim 6,
Wherein the spiral bars of the upper and lower mixer portions are offset from each other, wherein the iron-containing residue is converted into a stable form using a neutralizer. The method according to claim 5 or 6,
The spiral bars (12,13) surround the shaft (11) twice or twice, the apparatus for converting iron-containing residues into a stable form using neutralizing agents. The method according to claim 5 or 6,
Wherein the angle of the pitch of the spiral bars relative to the horizontal is between 15 and 45 degrees, preferably between 25 and 35 degrees, wherein the iron-containing residue is converted into a stable form using a neutralizing agent. The method according to claim 5 or 6,
The support arms 14 in the mixer 9, 10 are characterized in that they form an angle of 0 to 65 ° with respect to the horizontal, depending on the position of the support arm in the mixer or portion of the mixer. Method for switching to a stable form using. The method according to claim 5 or 6,
Wherein the ratio of the diameter of the mixer to the diameter of the stabilization or homogenization reactor is between 0.85 and 0.95, wherein the iron-containing residue is converted into a stable form using a neutralizing agent. The method of claim 5, wherein
Guide plates are installed in the upper side of the stabilization or homogenization reactor 3, the guide plates being oriented inclined inwardly from the edges of the reactor to guide slurry flow, and 3-8% of the diameter of the reactor. An apparatus for converting an iron-containing residue into a stable form using a neutralizing agent, characterized by extending inwardly by a phosphorus distance.

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